It's odd I saw this the same week as Mouse Hunt. Not that they have much in common, mind, but neither film seems to grasp the beauty of simplicity, and have enough faith in their core idea to believe it can sustain a whole movie. In Undead, this is more surprising: Night of the Living Dead proved the simplest idea, a small group of people trapped in a house by zombies, can not only work, it can lead to among the most influential horror films of all time. But perhaps the creators wanted to avoid comparisons, and opted to divert half-way through into an alien abduction/attack storyline. It's a shame, since that works less well than the simple, straightforward "spam in a cabin" elements. Meteorites land in the small Australian town of Berkeley, sparking an epidemic of, er, zombieness. What more do you need?
And yes, the first half is great, full of imaginative splatter and great characters that recall the early work of Peter Jackson. A local beauty queen; the town loonie and his large arsenal; a pair of ineffective cops; you know the kind of motley crew involved. However, when the film veers off to explain the cause, both of the zombies and the other odd happenings (such as the giant wall now surrounding the town), it struggles to hold attention. This is less due to technical aspects - indeed, they're remarkable, given most FX were done on the directors' laptop - more that explanation is unnecessary (as both Night and Shaun proved), and in this case, add to the film less than diverting from it. It's as if, lacking confidence in their skills, they tried to appeal to SF fans as well as horror ones. As a result, this is only a small wonder, rather than the cult classic which the opening had the potential to attain.